Friction clutches of this sort, which are combined, for example, into a double clutch, are known, for example, from DE 10 2009 005 743 A1. A shared counter-pressure plate is provided here, to which a non-rotating and axially movable pressing plate of a friction clutch in each case is assigned from each side. Both friction clutches are pressure-engaged by means of a lever spring each, which are situated on one side of the double clutch on both sides of a cover part, which is firmly connected to the counter-pressure plate and to this end are braced between the latter and the pressing plate. At the same time, one friction clutch is impinged upon directly by the lever spring assigned to it, and the other is acted upon by means of a tie rod which is connected to the pressing plate, which overlaps the counter-pressure plate and the cover part and enters into operative engagement with the lever spring which is assigned to the latter, so that when the radially inner lever tips are acted upon axially by means of an actuating system each in the direction of the counter-pressure plate, the one friction clutch is pressure-engaged directly by the lever spring and the other friction clutch is tension-engaged by means of the tie rod.
At the same time, both friction clutches have a self-adjusting adjusting device to compensate for the wear of the friction lining situated between the counter-pressure plate and the pressing plate, which is designed in the nature of a diaphragm spring lever assembly of DE 10 2008 010 997 A1. At the same time, a drive spring in the form of an open ring is situated on radially oriented levers of the lever spring distributed around the circumference of a ring-shaped power rim. The drive spring is connected to the lever spring through sensing tongues attached to the levers. The drive spring changes its circumference depending on the changing shape of the lever spring across an engagement path, there being a pawl situated at one end, which meshes with a pinion that is rotatably fastened to the lever spring. On the other side of the lever spring a worm gear is provided on the pinion, which drives a component provided with ramps that rise in the circumferential direction, which is operatively provided between lever spring and pressing plate, or between lever spring and tie rod. If the engagement path is elevated due to wear of the friction linings, a more pronounced deformation of the lever spring occurs when the friction clutch is in the engaged state, so that the circumference of the drive spring is reduced and the pawl jumps over one or more teeth of the pinion, and as the friction clutch disengages, the simultaneous pre-tensioning of the drive spring twists the freed component, so that the ramps, which are turned by a specified amount, compensate for the wear.
The friction linings, which form the frictional engagement with the opposing frictional surfaces of the counter-pressure plate and the pressing plate, are provided with a lining resiliency against each other, which along with the leaf springs, which receive the pressing plate non-rotatingly and axially movably on the counter-pressure plate or on the cover part when the friction clutch engages, counteract the engaging force of the actuating system. In order to compensate at least partially for the lining resiliency in the area of the friction clutch which transmits maximum torque, in the German patent application 10 2011 084 840.1, not previously published, a compensation spring is proposed, situated between the pressing plate of the counter-pressure plate or cover part and the pressing plate, which may be designed, for example, as an overtensioned diaphragm spring. The characteristic curve of the lining resiliency can change due to aging, setting processes and the like, so that the compensation spring fulfills the desired compensation function of partial or total compensation only insufficiently beyond the service life. As a result, an engagement force behavior of the friction clutch is subject to fluctuations over the service life.